Greenhouses are an excellent way to grow food in a controlled environment. By regulating environmental factors and blocking out pests, vegetable yields are increased significantly. But traditional greenhouses, made with rigid materials and glass, are expensive. You can expect to spend tens of thousands on greenhouses like these:

In the 1960s, polyethylene film in wide sheets became available. This set off a revolution in greenhouse design—particularly in the area of cost.

An unknown inventor figured out it was way cheaper to use inexpensive and easily bendable tubing, like PVC pipe, to build a skeletal Quonset hut. This could then be wrapped in the polyethylene film.

Compared to glass, polyethylene film is cheaper up front, easier to install, and cheaper to replace. These two innovations—the film and the "hoop house" design—made greenhouses affordable for the masses.

Not all hoop houses were made with PVC, with some preferring metal conduit. But the design is the same, regardless of the tubing type: Bent tubing for a row of hoops, and straight tubing run longitudinally to serve as purlins. This ingenious shape is sturdy, offers a measure of wind resistance and is highly economical.

The next issue that saw refinement was the connection method between the hoops and the purlins. The earliest builders simply drilled holes through both, and connected them with a carriage bolt. This proved to be laborious, requiring skilled accuracy to drill the holes. It was also cumbersome, in an era when drills still needed to be plugged into something.

Crafty builders turned to plumbing supply stores to use pipe clamps instead. These eventually morphed into purpose-designed cross connectors like these:

Those were an improvement over the drill-and-carriage-bolt method; if you made a mistake in placement, you could simply slide the connector to the correct location and re-tighten it. But there was room for improvement yet, as these connectors required the installer to use tools.

That improvement came in the form of these wire hoop-to-purlin connectors. They're pure form-follows-function, can be slid around easily for positioning, and can be installed without the use of tools. They're also cheap as chips.

These examples of the exploitation of material properties—for the polyethylene film, the PVC tubing and the wire clips—ought be taught to all industrial design students. These innovations reduced cost, increased access, eased installation, and used less material than earlier solutions. Design at its finest.